python - 弱引用和 __slots__

Question

考虑以下代码:

from weakref import ref

class Klass(object):
    # __slots__ = ['foo']
    def __init__(self):
        self.foo = 'bar'

k = Klass()
r = ref(k)

它可以工作，但是当我取消注释 __slots__ 时，它会因 TypeError: "cannot create weak reference to 'Klass' object" 在 Python 2.6 下中断。

请问，有谁知道这是 Python 和 __slots__ 的固有限制还是错误？如何解决？

Answer 1

Without a __weakref__ variable for each instance, classes defining __slots__ do not support weak references to its instances. If weak reference support is needed, then add __weakref__ to the sequence of strings in the __slots__ declaration.

来自 Python documentation .

如果您将 __weakref__ 添加到 __slots__，您的代码将起作用:

>>> from weakref import ref
>>>
>>> class Klass(object):
>>>     __slots__ = ['foo', '__weakref__']
>>>     def __init__(self):
>>>         self.foo = 'bar'
>>> k = Klass()
>>> k
 => <__main__.Klass object at ...>
>>> r = ref(k)
>>> r
 => <weakref at ...; to 'Klass' at ...>